1. Field of the Invention
The invention relates to a semiconductor device structure and a circuit structure. More particularly, the invention relates to a transistor structure and a driving circuit structure.
2. Description of Related Art
Among various flat panel displays, thin film transistor liquid crystal displays (TFT-LCD) characterized by great space utilization, low power consumption, non-radiation, and low electromagnetic interference gain popularity among consumers. The TFT-LCD is mainly constituted by an active array substrate, a color filter substrate, and a liquid crystal layer sandwiched between the two substrates. The active array substrate has an active region and a peripheral circuit region. An active array is located within the active region, and a driving circuit is located within the peripheral circuit region.
A TFT with a high width-to-length (W/L) ratio of the channel is often employed in the driving circuit within the peripheral circuit region, for instance. In general, an on-current Ion of the TFT is in direct proportion to the W/L ratio, and the on-current Ion satisfies the following equation:Ion=U*W/L(VG−Vth)VD 
Here, U refers to carrier mobility, W denotes the channel width, L denotes the channel length, VG represents a gate voltage, Vth refers to a threshold voltage, and VD refers to a drain voltage. According to said equation, the increase in the channel width and the decrease in the channel length may increase the W/L ratio and raise the on-current Ion. Nonetheless, when the channel width is increased, and the channel length is decreased, the notable self-heating effect of the TFT may deteriorate the stability and reliability of the TFT.